Gel cushions as seals or pads have long been known. They are used for example in the case of bicycle saddles, cushions and seats for uniform load distribution or are used in respiratory masks of a medical or industrial kind in the sealing and padding area that is up against the user's face.
These seals and pads are intended to be soft, elastic and pliable. It is usually desired that, after compressive loading during use, they revert to their original shape, in order to be able to perform their function again in the same way the next time they are used.
Elastic and gel-like materials have been found to be very well suited for padding and sealing materials, which are intended to produce a pleasing, softly padded feel for the user and at the same time provide a good permanent sealing effect by a certain elasticity and restoring force. Silicones and polyurethanes are used to a great extent.
The utility model DE 202 17 653 U1 discloses a gel body of a soft silicone gel that is surrounded by an outer skin of silicone or PU film and is connected to a carrier part by way of a harder intermediate part.
DE 696 34 431 T2 describes inter alia a facial seal for a respiratory mask comprising an annular sealing part of a viscoelastic polyurethane polymer with an elasticity similar to human fat tissue and a covering of the otherwise tacky polymer by a urethane film that is possibly thermoformed or applied by spraying or dipping. At 0.05 to 0.25 mm, this covering film is kept very thin in order not to change the elastic properties of the annular sealing body.
Elastic polyurethanes offer mechanical properties that can be set very well for the intended use. An inherent tackiness often necessitates a covering film, as described above. The film is intended to be thin and tear-resistant, but not obtrusive in use. This problem has not yet been fully solved in the prior art. There are many polyurethane compounds that cannot be replicated in their elastic and shape-changing behavior by the film surrounding them.
As a thin sprayed film, the aforementioned polyurethane covering film is capable of adapting itself under compressive loading to any movement of the viscoelastic polyurethane, but this does not apply to tensile loads. They may cause the film to tear. Sufficiently flexible PVC films contain too much plasticizer, with the accompanying disadvantages. Polyurethanes are generally incompatible with silicones, which are also used as release agents, so that detachments may occur at the interface.